I. Field
The present disclosure relates generally to communication, and more specifically to techniques for supporting positioning.
II. Background
It is often desirable, and sometimes necessary, to know the location of a terminal, e.g., a cellular phone. The terms “location” and “position” are synonymous and are used interchangeably herein. For example, a location services (LCS) client may desire to know the location of the terminal and may communicate with a location center in order to request the location of the terminal The location center and the terminal may then exchange messages, as necessary, to obtain a location estimate for the terminal The location center may then return the location estimate to the LCS client.
The location of the terminal may be estimated based on pseudo-ranges for a sufficient number of satellites in a global navigation satellite system (GNSS) and the known locations of the satellites. The pseudo-ranges for the satellites may be determined by the terminal based on signals transmitted by the satellites. The pseudo-ranges may have errors due to various sources such as (i) propagation delays of the satellite signals through the ionosphere and troposphere, (ii) errors in ephemeris data describing the locations and velocities of the satellites, (iii) clock drift on the satellites, and/or (iv) pseudo-random errors deliberately introduced in the satellite signals via a process referred to as selective availability (SA). It may be desirable to obtain a reliable location estimate for the terminal in light of the errors in the pseudo-ranges.